There has been a long-felt need for systems that accurately and non-invasively measure one or more analytes in a sample, especially for a variety of healthcare procedures. Spectroscopic systems for optically measuring blood analytes, including Raman spectroscopy for measuring glucose levels in blood or tissue of a patient, using a light source such as a laser or a laser diode, are described in U.S. Pat. No. 7,039,448 by Schlegel et al. and in U.S. Patent Publication No. 2008/0316466 by Higgins et al., both assigned to DIRAmed, LLC. Other non-invasive optical techniques for measuring one or more blood components are disclosed in U.S. Patent Publication Nos. 2006/0276697 by Demuth et al., 2007/0049809 by Bechtel et al. and 2007/0060806 by Hunter et al., for example.
In general, spectroscopy typically involves illuminating a sample, such as a portion of a patient's skin, through a measurement window with a beam of optical radiation, preferably coherent monochromatic light from a laser or a laser diode within a spectrometer, and analyzing a selected spectrum of light returned from the sample to the spectrometer. In certain types of spectroscopy, such as Raman spectroscopy, only the light coming back from slightly penetrating the sample contains the relevant spectrum. Light that reflects or bounces off the sample is largely noise rather than useful signal. It is often challenging to achieve an acceptable signal-to-noise ratio, even with well-calibrated systems.
Precise and repeatable calibration of spectrometers is critical to identifying affect proper analysis of light returned from a sample. Conventional calibration typically is a manual process using known standards such as certain chemicals or light sources that are placed at the exterior side of the measurement window in the same location where samples are normally placed.
User safety is another critical issue when using optical radiation sources, especially when a person's eyes may be exposed to potentially harmful radiation. Important guidelines have been set forth by the Center for Devices and Radiological Health (CDRH) of the Food and Drug Administration (FDA) when diagnostic measurements or other medical procedures are performed on a patient. These CDRH guidelines are in addition to those of the American National Standards Institute (ANSI) and include system lockouts, light-tight enclosures, protective goggles and warning labels. These mitigating techniques can be very bulky and encumbering to users.
Internal shutters have been commonly utilized m cameras, spectrometers and other systems requiring control of light into or out of housings. Laser safety shutters, for example, are available from a number of sources including Electro-Optical Products Corporation of Ridgewood, N.Y.
It is therefore desirable to eliminate the need for users to wear protective goggles while using and calibrating spectrometers, and to simplify calibration procedures.